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Date:   Tue, 24 Oct 2023 00:57:47 +0200
From:   Danilo Krummrich <dakr@redhat.com>
To:     Boris Brezillon <boris.brezillon@collabora.com>
Cc:     airlied@gmail.com, daniel@ffwll.ch, matthew.brost@intel.com,
        christian.koenig@amd.com, faith.ekstrand@collabora.com,
        luben.tuikov@amd.com, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH drm-misc-next v2] drm/sched: implement dynamic job-flow
 control
Message-ID: <ZTb6azSfTV+LRGYu@pollux>
References: <20231009223554.11846-1-dakr@redhat.com>
 <20231010094151.4c116058@collabora.com>
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In-Reply-To: <20231010094151.4c116058@collabora.com>
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On Tue, Oct 10, 2023 at 09:41:51AM +0200, Boris Brezillon wrote:
> On Tue, 10 Oct 2023 00:35:53 +0200
> Danilo Krummrich <dakr@redhat.com> wrote:
> 
> > Currently, job flow control is implemented simply by limiting the number
> > of jobs in flight. Therefore, a scheduler is initialized with a
> > submission limit that corresponds to the number of jobs which can be
> > sent to the hardware.
> > 
> > This implies that for each job, drivers need to account for the maximum
> > job size possible in order to not overflow the ring buffer.
> > 
> > However, there are drivers, such as Nouveau, where the job size has a
> > rather large range. For such drivers it can easily happen that job
> > submissions not even filling the ring by 1% can block subsequent
> > submissions, which, in the worst case, can lead to the ring run dry.
> > 
> > In order to overcome this issue, allow for tracking the actual job size
> > instead of the number of jobs. Therefore, add a field to track a job's
> > submission credits, which represents the number of credits a job
> > contributes to the scheduler's submission limit.
> > 
> > Signed-off-by: Danilo Krummrich <dakr@redhat.com>
> > ---
> > Changes in V2:
> > ==============
> >   - fixed up influence on scheduling fairness due to consideration of a job's
> >     size
> >     - If we reach a ready entity in drm_sched_select_entity() but can't actually
> >       queue a job from it due to size limitations, just give up and go to sleep
> >       until woken up due to a pending job finishing, rather than continue to try
> >       other entities.
> >   - added a callback to dynamically update a job's credits (Boris)
> >   - renamed 'units' to 'credits'
> >   - fixed commit message and comments as requested by Luben
> > ---
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_job.c       |   2 +-
> >  drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c  |   2 +-
> >  drivers/gpu/drm/lima/lima_sched.c             |   2 +-
> >  drivers/gpu/drm/msm/msm_gem_submit.c          |   2 +-
> >  drivers/gpu/drm/nouveau/nouveau_sched.c       |   2 +-
> >  drivers/gpu/drm/panfrost/panfrost_drv.c       |   2 +-
> >  .../gpu/drm/scheduler/gpu_scheduler_trace.h   |   2 +-
> >  drivers/gpu/drm/scheduler/sched_entity.c      |   5 +-
> >  drivers/gpu/drm/scheduler/sched_main.c        | 101 +++++++++++++-----
> >  drivers/gpu/drm/v3d/v3d_gem.c                 |   2 +-
> >  include/drm/gpu_scheduler.h                   |  33 ++++--
> >  11 files changed, 115 insertions(+), 40 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
> > index 78476bc75b4e..d54daaf64bf1 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
> > @@ -115,7 +115,7 @@ int amdgpu_job_alloc(struct amdgpu_device *adev, struct amdgpu_vm *vm,
> >  	if (!entity)
> >  		return 0;
> >  
> > -	return drm_sched_job_init(&(*job)->base, entity, owner);
> > +	return drm_sched_job_init(&(*job)->base, entity, 1, owner);
> >  }
> >  
> >  int amdgpu_job_alloc_with_ib(struct amdgpu_device *adev,
> > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c b/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
> > index 45403ea38906..74a446711207 100644
> > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
> > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
> > @@ -538,7 +538,7 @@ int etnaviv_ioctl_gem_submit(struct drm_device *dev, void *data,
> >  
> >  	ret = drm_sched_job_init(&submit->sched_job,
> >  				 &ctx->sched_entity[args->pipe],
> > -				 submit->ctx);
> > +				 1, submit->ctx);
> >  	if (ret)
> >  		goto err_submit_put;
> >  
> > diff --git a/drivers/gpu/drm/lima/lima_sched.c b/drivers/gpu/drm/lima/lima_sched.c
> > index 50c2075228aa..5dc6678e1eb9 100644
> > --- a/drivers/gpu/drm/lima/lima_sched.c
> > +++ b/drivers/gpu/drm/lima/lima_sched.c
> > @@ -123,7 +123,7 @@ int lima_sched_task_init(struct lima_sched_task *task,
> >  	for (i = 0; i < num_bos; i++)
> >  		drm_gem_object_get(&bos[i]->base.base);
> >  
> > -	err = drm_sched_job_init(&task->base, &context->base, vm);
> > +	err = drm_sched_job_init(&task->base, &context->base, 1, vm);
> >  	if (err) {
> >  		kfree(task->bos);
> >  		return err;
> > diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> > index 3f1aa4de3b87..6d230c38e4f5 100644
> > --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> > +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> > @@ -48,7 +48,7 @@ static struct msm_gem_submit *submit_create(struct drm_device *dev,
> >  		return ERR_PTR(ret);
> >  	}
> >  
> > -	ret = drm_sched_job_init(&submit->base, queue->entity, queue);
> > +	ret = drm_sched_job_init(&submit->base, queue->entity, 1, queue);
> >  	if (ret) {
> >  		kfree(submit->hw_fence);
> >  		kfree(submit);
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.c b/drivers/gpu/drm/nouveau/nouveau_sched.c
> > index f26a814a9920..e991426d86e4 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_sched.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_sched.c
> > @@ -89,7 +89,7 @@ nouveau_job_init(struct nouveau_job *job,
> >  
> >  	}
> >  
> > -	ret = drm_sched_job_init(&job->base, &entity->base, NULL);
> > +	ret = drm_sched_job_init(&job->base, &entity->base, 1, NULL);
> >  	if (ret)
> >  		goto err_free_chains;
> >  
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > index b834777b409b..54d1c19bea84 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > @@ -274,7 +274,7 @@ static int panfrost_ioctl_submit(struct drm_device *dev, void *data,
> >  
> >  	ret = drm_sched_job_init(&job->base,
> >  				 &file_priv->sched_entity[slot],
> > -				 NULL);
> > +				 1, NULL);
> >  	if (ret)
> >  		goto out_put_job;
> >  
> > diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h b/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
> > index 3143ecaaff86..2e4ffdecc5dc 100644
> > --- a/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
> > +++ b/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
> > @@ -51,7 +51,7 @@ DECLARE_EVENT_CLASS(drm_sched_job,
> >  			   __assign_str(name, sched_job->sched->name);
> >  			   __entry->job_count = spsc_queue_count(&entity->job_queue);
> >  			   __entry->hw_job_count = atomic_read(
> > -				   &sched_job->sched->hw_rq_count);
> > +				   &sched_job->sched->submission_count);
> >  			   ),
> >  	    TP_printk("entity=%p, id=%llu, fence=%p, ring=%s, job count:%u, hw job count:%d",
> >  		      __entry->entity, __entry->id,
> > diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> > index 437c50867c99..6395090d5784 100644
> > --- a/drivers/gpu/drm/scheduler/sched_entity.c
> > +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> > @@ -401,7 +401,8 @@ static void drm_sched_entity_wakeup(struct dma_fence *f,
> >  		container_of(cb, struct drm_sched_entity, cb);
> >  
> >  	drm_sched_entity_clear_dep(f, cb);
> > -	drm_sched_wakeup_if_can_queue(drm_sched_entity_to_scheduler(entity));
> > +	drm_sched_wakeup_if_can_queue(drm_sched_entity_to_scheduler(entity),
> > +				      entity);
> >  }
> >  
> >  /**
> > @@ -645,7 +646,7 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
> >  		if (fifo)
> >  			drm_sched_rq_update_fifo(entity, submit_ts);
> >  
> > -		drm_sched_wakeup_if_can_queue(sched);
> > +		drm_sched_wakeup_if_can_queue(sched, entity);
> >  	}
> >  }
> >  EXPORT_SYMBOL(drm_sched_entity_push_job);
> > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> > index 88ef8be2d3c7..da86dd0782d6 100644
> > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > @@ -93,6 +93,9 @@ int drm_sched_policy_default = DRM_SCHED_POLICY_FIFO;
> >  MODULE_PARM_DESC(sched_policy, "Specify the scheduling policy for entities on a run-queue, " __stringify(DRM_SCHED_POLICY_RR) " = Round Robin, " __stringify(DRM_SCHED_POLICY_FIFO) " = FIFO (default).");
> >  module_param_named(sched_policy, drm_sched_policy_default, int, 0444);
> >  
> > +static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched,
> > +				struct drm_sched_entity *entity);
> 
> Nit: can we move the function instead of adding this forward
> declaration? I know it tends to screw up the diff, so maybe do it in 2
> steps.

Sure, gonna move it up.

> 
> > +
> >  static __always_inline bool drm_sched_entity_compare_before(struct rb_node *a,
> >  							    const struct rb_node *b)
> >  {
> > @@ -212,13 +215,15 @@ void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
> >  /**
> >   * drm_sched_rq_select_entity_rr - Select an entity which could provide a job to run
> >   *
> > + * @sched: the gpu scheduler
> >   * @rq: scheduler run queue to check.
> >   * @dequeue: dequeue selected entity
> >   *
> >   * Try to find a ready entity, returns NULL if none found.
> >   */
> >  static struct drm_sched_entity *
> > -drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq, bool dequeue)
> > +drm_sched_rq_select_entity_rr(struct drm_gpu_scheduler *sched,
> > +			      struct drm_sched_rq *rq, bool dequeue)
> >  {
> >  	struct drm_sched_entity *entity;
> >  
> > @@ -228,6 +233,12 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq, bool dequeue)
> >  	if (entity) {
> >  		list_for_each_entry_continue(entity, &rq->entities, list) {
> >  			if (drm_sched_entity_is_ready(entity)) {
> > +				/* If we can't queue yet, preserve the current
> > +				 * entity in terms of fairness.
> > +				 */
> > +				if (!drm_sched_can_queue(sched, entity))
> > +					goto out;
> > +
> >  				if (dequeue) {
> >  					rq->current_entity = entity;
> >  					reinit_completion(&entity->entity_idle);
> > @@ -239,8 +250,13 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq, bool dequeue)
> >  	}
> >  
> >  	list_for_each_entry(entity, &rq->entities, list) {
> > -
> >  		if (drm_sched_entity_is_ready(entity)) {
> > +			/* If we can't queue yet, preserve the current entity in
> > +			 * terms of fairness.
> > +			 */
> > +			if (!drm_sched_can_queue(sched, entity))
> > +				goto out;
> > +
> >  			if (dequeue) {
> >  				rq->current_entity = entity;
> >  				reinit_completion(&entity->entity_idle);
> > @@ -253,21 +269,23 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq, bool dequeue)
> >  			break;
> >  	}
> >  
> > +out:
> >  	spin_unlock(&rq->lock);
> > -
> >  	return NULL;
> >  }
> >  
> >  /**
> >   * drm_sched_rq_select_entity_fifo - Select an entity which provides a job to run
> >   *
> > + * @sched: the gpu scheduler
> >   * @rq: scheduler run queue to check.
> >   * @dequeue: dequeue selected entity
> >   *
> >   * Find oldest waiting ready entity, returns NULL if none found.
> >   */
> >  static struct drm_sched_entity *
> > -drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq, bool dequeue)
> > +drm_sched_rq_select_entity_fifo(struct drm_gpu_scheduler *sched,
> > +				struct drm_sched_rq *rq, bool dequeue)
> >  {
> >  	struct rb_node *rb;
> >  
> > @@ -277,6 +295,15 @@ drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq, bool dequeue)
> >  
> >  		entity = rb_entry(rb, struct drm_sched_entity, rb_tree_node);
> >  		if (drm_sched_entity_is_ready(entity)) {
> > +			/* If we can't queue yet, don't pick another entity
> > +			 * which's job might fit and wait until we got space for
> > +			 * this one in terms of fairness.
> > +			 */
> > +			if (!drm_sched_can_queue(sched, entity)) {
> > +				spin_unlock(&rq->lock);
> > +				return NULL;
> > +			}
> > +
> >  			if (dequeue) {
> >  				rq->current_entity = entity;
> >  				reinit_completion(&entity->entity_idle);
> > @@ -302,13 +329,32 @@ static void drm_sched_run_job_queue(struct drm_gpu_scheduler *sched)
> >  /**
> >   * drm_sched_can_queue -- Can we queue more to the hardware?
> >   * @sched: scheduler instance
> > + * @entity: the scheduler entity
> >   *
> > - * Return true if we can push more jobs to the hw, otherwise false.
> > + * Return true if we can push at least one more job from @entity, false
> > + * otherwise.
> >   */
> > -static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched)
> > +static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched,
> > +				struct drm_sched_entity *entity)
> >  {
> > -	return atomic_read(&sched->hw_rq_count) <
> > -		sched->hw_submission_limit;
> > +	struct drm_sched_job *s_job;
> > +
> > +	s_job = to_drm_sched_job(spsc_queue_peek(&entity->job_queue));
> > +	if (!s_job)
> > +		return false;
> > +
> > +	if (sched->ops->update_job_credits) {
> > +		u32 credits = sched->ops->update_job_credits(s_job);
> > +
> > +		if (credits)
> > +			s_job->submission_credits = credits;
> > +	}
> > +
> > +	WARN_ON(s_job->submission_credits > sched->submission_limit);
> > +
> > +	return (sched->submission_limit -
> > +		atomic_read(&sched->submission_count)) >=
> 
> Nit: might be clearer with a dummy drm_sched_available_credits()
> helper:

Sure, why not.

> 
> static u32
> drm_sched_available_credits(struct drm_gpu_scheduler *sched)
> {
> 	return sched->submission_limit -
> 	       atomic_read(&sched->submission_count);
> }
> 
> > +		s_job->submission_credits;
> >  }
> >  
> >  /**
> > @@ -325,12 +371,10 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched, bool dequeue)
> >  	struct drm_sched_entity *entity;
> >  	int i;
> >  
> > -	if (!drm_sched_can_queue(sched))
> > -		return NULL;
> > -
> >  	if (sched->single_entity) {
> >  		if (!READ_ONCE(sched->single_entity->stopped) &&
> > -		    drm_sched_entity_is_ready(sched->single_entity))
> > +		    drm_sched_entity_is_ready(sched->single_entity) &&
> > +		    drm_sched_can_queue(sched, sched->single_entity))
> >  			return sched->single_entity;
> >  
> >  		return NULL;
> > @@ -339,9 +383,11 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched, bool dequeue)
> >  	/* Kernel run queue has higher priority than normal run queue*/
> >  	for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= DRM_SCHED_PRIORITY_MIN; i--) {
> >  		entity = sched->sched_policy == DRM_SCHED_POLICY_FIFO ?
> > -			drm_sched_rq_select_entity_fifo(&sched->sched_rq[i],
> > +			drm_sched_rq_select_entity_fifo(sched,
> > +							&sched->sched_rq[i],
> >  							dequeue) :
> > -			drm_sched_rq_select_entity_rr(&sched->sched_rq[i],
> > +			drm_sched_rq_select_entity_rr(sched,
> > +						      &sched->sched_rq[i],
> >  						      dequeue);
> >  		if (entity)
> >  			break;
> > @@ -399,7 +445,7 @@ static void drm_sched_job_done(struct drm_sched_job *s_job, int result)
> >  	struct drm_sched_fence *s_fence = s_job->s_fence;
> >  	struct drm_gpu_scheduler *sched = s_fence->sched;
> >  
> > -	atomic_dec(&sched->hw_rq_count);
> > +	atomic_sub(s_job->submission_credits, &sched->submission_count);
> >  	atomic_dec(sched->score);
> >  
> >  	trace_drm_sched_process_job(s_fence);
> > @@ -622,7 +668,8 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
> >  					      &s_job->cb)) {
> >  			dma_fence_put(s_job->s_fence->parent);
> >  			s_job->s_fence->parent = NULL;
> > -			atomic_dec(&sched->hw_rq_count);
> > +			atomic_sub(s_job->submission_credits,
> > +				   &sched->submission_count);
> >  		} else {
> >  			/*
> >  			 * remove job from pending_list.
> > @@ -683,7 +730,7 @@ void drm_sched_start(struct drm_gpu_scheduler *sched, bool full_recovery)
> >  	list_for_each_entry_safe(s_job, tmp, &sched->pending_list, list) {
> >  		struct dma_fence *fence = s_job->s_fence->parent;
> >  
> > -		atomic_inc(&sched->hw_rq_count);
> > +		atomic_add(s_job->submission_credits, &sched->submission_count);
> >  
> >  		if (!full_recovery)
> >  			continue;
> > @@ -764,6 +811,8 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs);
> >   * drm_sched_job_init - init a scheduler job
> >   * @job: scheduler job to init
> >   * @entity: scheduler entity to use
> > + * @submission_credits: the number of credits this job contributes to the
> > + * schdulers submission limit
> >   * @owner: job owner for debugging
> >   *
> >   * Refer to drm_sched_entity_push_job() documentation
> > @@ -781,6 +830,7 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs);
> >   */
> >  int drm_sched_job_init(struct drm_sched_job *job,
> >  		       struct drm_sched_entity *entity,
> > +		       u32 submission_credits,
> >  		       void *owner)
> >  {
> >  	if (!entity->rq && !entity->single_sched)
> > @@ -792,6 +842,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
> >  		return -ENOMEM;
> >  
> >  	INIT_LIST_HEAD(&job->list);
> > +	job->submission_credits = submission_credits ? submission_credits : 1;
> >  
> >  	xa_init_flags(&job->dependencies, XA_FLAGS_ALLOC);
> >  
> > @@ -1004,12 +1055,14 @@ EXPORT_SYMBOL(drm_sched_job_cleanup);
> >  /**
> >   * drm_sched_wakeup_if_can_queue - Wake up the scheduler
> >   * @sched: scheduler instance
> > + * @entity: the scheduler entity
> >   *
> >   * Wake up the scheduler if we can queue jobs.
> >   */
> > -void drm_sched_wakeup_if_can_queue(struct drm_gpu_scheduler *sched)
> > +void drm_sched_wakeup_if_can_queue(struct drm_gpu_scheduler *sched,
> > +				   struct drm_sched_entity *entity)
> >  {
> > -	if (drm_sched_can_queue(sched))
> > +	if (drm_sched_can_queue(sched, entity))
> >  		drm_sched_run_job_queue(sched);
> >  }
> >  
> > @@ -1147,7 +1200,7 @@ static void drm_sched_run_job_work(struct work_struct *w)
> >  
> >  	s_fence = sched_job->s_fence;
> >  
> > -	atomic_inc(&sched->hw_rq_count);
> > +	atomic_add(sched_job->submission_credits, &sched->submission_count);
> >  	drm_sched_job_begin(sched_job);
> >  
> >  	trace_drm_run_job(sched_job, entity);
> > @@ -1183,7 +1236,7 @@ static void drm_sched_run_job_work(struct work_struct *w)
> >   * @ops: backend operations for this scheduler
> >   * @submit_wq: workqueue to use for submission. If NULL, an ordered wq is
> >   *	       allocated and used
> > - * @hw_submission: number of hw submissions that can be in flight
> > + * @max_submission_credits: number of submission credits that can be in flight
> >   * @hang_limit: number of times to allow a job to hang before dropping it
> >   * @timeout: timeout value in jiffies for the scheduler
> >   * @timeout_wq: workqueue to use for timeout work. If NULL, the system_wq is
> > @@ -1198,7 +1251,7 @@ static void drm_sched_run_job_work(struct work_struct *w)
> >  int drm_sched_init(struct drm_gpu_scheduler *sched,
> >  		   const struct drm_sched_backend_ops *ops,
> >  		   struct workqueue_struct *submit_wq,
> > -		   unsigned hw_submission, unsigned hang_limit,
> > +		   unsigned max_submission_credits, unsigned hang_limit,
> >  		   long timeout, struct workqueue_struct *timeout_wq,
> >  		   atomic_t *score, const char *name,
> >  		   enum drm_sched_policy sched_policy,
> > @@ -1211,7 +1264,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
> >  
> >  	sched->ops = ops;
> >  	sched->single_entity = NULL;
> > -	sched->hw_submission_limit = hw_submission;
> > +	sched->submission_limit = max_submission_credits;
> >  	sched->name = name;
> >  	if (!submit_wq) {
> >  		sched->submit_wq = alloc_ordered_workqueue(name, 0);
> > @@ -1238,7 +1291,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
> >  	init_waitqueue_head(&sched->job_scheduled);
> >  	INIT_LIST_HEAD(&sched->pending_list);
> >  	spin_lock_init(&sched->job_list_lock);
> > -	atomic_set(&sched->hw_rq_count, 0);
> > +	atomic_set(&sched->submission_count, 0);
> >  	INIT_DELAYED_WORK(&sched->work_tdr, drm_sched_job_timedout);
> >  	INIT_WORK(&sched->work_run_job, drm_sched_run_job_work);
> >  	INIT_WORK(&sched->work_free_job, drm_sched_free_job_work);
> > diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
> > index 2e94ce788c71..8479e5302f7b 100644
> > --- a/drivers/gpu/drm/v3d/v3d_gem.c
> > +++ b/drivers/gpu/drm/v3d/v3d_gem.c
> > @@ -417,7 +417,7 @@ v3d_job_init(struct v3d_dev *v3d, struct drm_file *file_priv,
> >  	job->free = free;
> >  
> >  	ret = drm_sched_job_init(&job->base, &v3d_priv->sched_entity[queue],
> > -				 v3d_priv);
> > +				 1, v3d_priv);
> >  	if (ret)
> >  		goto fail;
> >  
> > diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> > index 27f5778bbd6d..c4a53b259585 100644
> > --- a/include/drm/gpu_scheduler.h
> > +++ b/include/drm/gpu_scheduler.h
> > @@ -329,6 +329,8 @@ struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f);
> >   * @sched: the scheduler instance on which this job is scheduled.
> >   * @s_fence: contains the fences for the scheduling of job.
> >   * @finish_cb: the callback for the finished fence.
> > + * @submission_credits: the number of submission credits this job contributes to
> > + *                      the scheduler
> >   * @work: Helper to reschdeule job kill to different context.
> >   * @id: a unique id assigned to each job scheduled on the scheduler.
> >   * @karma: increment on every hang caused by this job. If this exceeds the hang
> > @@ -348,6 +350,8 @@ struct drm_sched_job {
> >  	struct drm_gpu_scheduler	*sched;
> >  	struct drm_sched_fence		*s_fence;
> >  
> > +	u32				submission_credits;
> > +
> >  	/*
> >  	 * work is used only after finish_cb has been used and will not be
> >  	 * accessed anymore.
> > @@ -471,6 +475,21 @@ struct drm_sched_backend_ops {
> >           * and it's time to clean it up.
> >  	 */
> >  	void (*free_job)(struct drm_sched_job *sched_job);
> > +
> > +	/**
> > +	 * @update_job_credits: Called once the scheduler is considering this
> > +	 * job for execution.
> > +	 *
> > +	 * Drivers may use this to update the job's submission credits, which is
> > +	 * useful to e.g. deduct the number of native fences which have been
> > +	 * signaled meanwhile.
> > +	 *
> > +	 * The callback must either return the new number of submission credits
> > +	 * for the given job, or zero if no update is required.
> 
> Any reason for having this special zero-means-no-update case? I mean,
> drivers could just return sched_job->submission_credits if nothing
> changed, and that would simplify the semantics IMHO. Another option, if

I think I just did this because I thought it's a clever way to get rid of the
need to deal with zero-sized jobs, which do not make much sense. In
drm_sched_job_init() passing a zero job size defaults to one, which I think is
reasonable. Doing the same thing here is more likely to hide a bug. However, the
same is probably true for 'zero means no update' though. Maybe we should just
WARN() in such a case.

> we want to avoid the sched_job->submission_credits assignment when
> nothing changes would be to make it a void function and let it update
> the sched_job->submission_credits directly.

Sure, that's an option as well. However, I'd probably prefer the new job size to
be the return value. Having to sanity check job->submission_credits afterwards
isn't that nice either.

> 
> > +	 *
> > +	 * This callback is optional.
> > +	 */
> > +	u32 (*update_job_credits)(struct drm_sched_job *sched_job);
> >  };
> >  
> >  /**
> > @@ -478,14 +497,14 @@ struct drm_sched_backend_ops {
> >   *
> >   * @ops: backend operations provided by the driver.
> >   * @single_entity: Single entity for the scheduler
> > - * @hw_submission_limit: the max size of the hardware queue.
> > + * @submission_limit: the maximim number of submission credits
> > + * @submission_count: the number of submission credits in flight
> 
> Now that we use the term credit at the job level, I'd recommend using
> it here as well, for consistency. Maybe
> s/submission_count/assigned_credits/ and
> s/submission_limit/max_credits/?

IIRC, Luben is proposing something similar. Gonna change that.

> 
> >   * @timeout: the time after which a job is removed from the scheduler.
> >   * @name: name of the ring for which this scheduler is being used.
> >   * @sched_rq: priority wise array of run queues.
> >   * @job_scheduled: once @drm_sched_entity_do_release is called the scheduler
> >   *                 waits on this wait queue until all the scheduled jobs are
> >   *                 finished.
> > - * @hw_rq_count: the number of jobs currently in the hardware queue.
> >   * @job_id_count: used to assign unique id to the each job.
> >   * @submit_wq: workqueue used to queue @work_run_job and @work_free_job
> >   * @timeout_wq: workqueue used to queue @work_tdr
> > @@ -511,12 +530,12 @@ struct drm_sched_backend_ops {
> >  struct drm_gpu_scheduler {
> >  	const struct drm_sched_backend_ops	*ops;
> >  	struct drm_sched_entity		*single_entity;
> > -	uint32_t			hw_submission_limit;
> > +	u32				submission_limit;
> > +	atomic_t			submission_count;
> >  	long				timeout;
> >  	const char			*name;
> >  	struct drm_sched_rq		sched_rq[DRM_SCHED_PRIORITY_COUNT];
> >  	wait_queue_head_t		job_scheduled;
> > -	atomic_t			hw_rq_count;
> >  	atomic64_t			job_id_count;
> >  	struct workqueue_struct		*submit_wq;
> >  	struct workqueue_struct		*timeout_wq;
> > @@ -539,7 +558,7 @@ struct drm_gpu_scheduler {
> >  int drm_sched_init(struct drm_gpu_scheduler *sched,
> >  		   const struct drm_sched_backend_ops *ops,
> >  		   struct workqueue_struct *submit_wq,
> > -		   uint32_t hw_submission, unsigned hang_limit,
> > +		   uint32_t max_submission_credits, unsigned hang_limit,
> >  		   long timeout, struct workqueue_struct *timeout_wq,
> >  		   atomic_t *score, const char *name,
> >  		   enum drm_sched_policy sched_policy,
> > @@ -548,6 +567,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
> >  void drm_sched_fini(struct drm_gpu_scheduler *sched);
> >  int drm_sched_job_init(struct drm_sched_job *job,
> >  		       struct drm_sched_entity *entity,
> > +		       u32 submission_credits,
> >  		       void *owner);
> 
> Nit: we keep adding parameters to functions like drm_sched_init() and
> drm_sched_job_init() and every time this implies patching all call
> sites to pass the new default value. In a sense, that's a good thing,
> because it forces driver maintainers to check that the patch does the
> right thing. But overall, it makes the driver code harder to read, in
> that it forces the reader to go check the function prototype to figure
> out what these magic 1 or NULL values mean. So, I wonder if we
> shouldn't move to a model where we pass struct drm_sched[_job]_params
> objects around:
> 
> 	const struct drm_sched_job_params params = {
> 		.entity = xxx,
> 		.submission_credits = xxx,
> 		.owner = THIS_MODULE,
> 	};
> 
> 	...
> 
> 	ret = drm_sched_job_init(job, &params);
> 
> It would also let us add new fields and pick the right default when
> this field is zero, thus preventing cross-driver updates when such a
> field is added.

Yes, the same is true for drm_sched_init() - that's something for a separate
patch though.

> 
> >  void drm_sched_job_arm(struct drm_sched_job *job);
> >  int drm_sched_job_add_dependency(struct drm_sched_job *job,
> > @@ -570,7 +590,8 @@ void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
> >  
> >  void drm_sched_tdr_queue_imm(struct drm_gpu_scheduler *sched);
> >  void drm_sched_job_cleanup(struct drm_sched_job *job);
> > -void drm_sched_wakeup_if_can_queue(struct drm_gpu_scheduler *sched);
> > +void drm_sched_wakeup_if_can_queue(struct drm_gpu_scheduler *sched,
> > +				   struct drm_sched_entity *entity);
> >  bool drm_sched_submit_ready(struct drm_gpu_scheduler *sched);
> >  void drm_sched_submit_stop(struct drm_gpu_scheduler *sched);
> >  void drm_sched_submit_start(struct drm_gpu_scheduler *sched);
>